1. Field of the Invention
Embodiments of the invention relate to a method for recording bursts on a disk and an apparatus adapted to perform the method. In particular, embodiments of the invention relate to a burst recording method adapted to erase edge-adjacent areas using a high frequency AC current generated by a circuit independent of a write channel circuit, and an apparatus adapted to perform the method.
This application claims priority to Korean Patent Application No. 10-2005-0106033, filed on Nov. 7, 2005, the subject matter of which is hereby incorporated by reference in its entirety.
2. Description of the Related Art
A hard disk drive (HDD) is a data storage device adapted to store data to and read data from at least one disk using a magnetic head. Developments in HDD technology are aimed at increasing the capacity, increasing the density, and reducing the size of an HDD; which increase the number of bits per inch (BPI) stored on a disk (i.e., the disk's storage density in the direction in which the disk rotates), increase the number of tracks per inch (TPI) in the disk (i.e., the disk's storage density in a radial direction), and also necessitate finer control of the position of the head of the HDD.
To read data from or write data to a desired position on a magnetic disk in an HDD, servo information is required in order to properly control the position of a head of the HDD relative to the disk.
FIG. 1 illustrates the configuration of a servo sector written on a disk.
Referring to FIG. 1, a servo sector 100 comprises a preamble field 102, a servo address mark/servo index mark (SAM/SIM) field 104, a gray code field 106, and a burst field 108. The preamble field 102 is used to determine a constant timing margin by allocating a gap to the beginning of the servo sector 100 and is used to determine a gain by automatic gain control (AGC). The SAM indicates the beginning of the servo sector 100, and the SIM provides disk one-revolution information. The gray code field 106 provides track and sector numbers, and the burst field 108 is used to obtain position information about a head that is separated from the center of a track (i.e., a head apart from the track center). In general, a four-burst method, which is a method using four types (i.e., kinds) of bursts (wherein the four burst types are A, B, C, and D), is used to control the position of a head.
FIG. 2 illustrates bursts A, B, C, and D written on the disk. Referring to FIG. 2, bursts of each of the four burst types A, B, C, and D are respectively written such that they are aligned differently along the tracks, and bursts of each of the four burst types A, B, C, and D are respectively written along different radii of the disk. For example, in FIG. 2, bursts A, C, and D are each at least partially disposed on an Nth track, and bursts B, C, and D are each at least partially disposed on an (N+1)th track. On the Nth track, burst A is aligned with the center of the track while burst C is shifted by ½ of a track towards the outer edge of the disk and burst D is shifted by ½ of a track towards the center of the disk. In addition, on the (N+1)th track, burst B is aligned with the center of the track while burst C is shifted by ½ of a track towards the center of the disk and burst D is shifted by ½ of a track towards the outer edge of the disk. Thus, in both the Nth and the (N+1)th tracks, bursts C and D are shifted in opposite directions with respect to one another.
A process for recording servo information including bursts on a disk is called a servo track write process. Servo track write (STW) methods include an offline STW method, a reference servo track copy method, etc.
To reduce the asymmetry of bursts with respect to radial directions on the disk and to reduce the distortion of the bursts, techniques for erasing areas of a track(s) adjacent to radial edges of a burst (i.e., for erasing both edges of the bursts in the radius direction) have been introduced. For example, a DC-erase method, which is a technique for erasing areas of a disk adjacent to radial edges of bursts (i.e., a technique of erasing both edges of bursts) using a DC current, is disclosed in Japanese Patent Publication No. 9-063217. As used herein, a “radial edge” of a burst is an edge of the burst that is disposed substantially along a radius of the disk, and an area of a track that is adjacent to a radial edge of a burst disposed at least partially on the track may be referred to herein as a “radial-edge-adjacent area.”
The DC-erase method can be a positive DC-erase method or a negative DC-erase method, wherein magnetic fields used for erasing in the positive and negative DC-erase methods have opposite directions.
In addition, an AC-erase method exists in which, unlike in the DC-erase method, radial-edge-adjacent areas are erased using a high frequency AC current. The high frequency AC current has a higher frequency than the current used to write the bursts (e.g., a frequency that is more than double the frequency of the current used to write the bursts).
FIG. 3 is a graph showing the effects of DC-erase methods and an AC-erase method. In FIG. 3, reference numeral 1 denotes a burst trajectory according to the positive DC-erase method, reference numeral 2 denotes a burst trajectory according to the negative DC-erase method, and reference numeral 3 denotes a burst trajectory according to the AC-erase method. In the graph illustrated in FIG. 3, the vertical axis indicates the amplitude of a burst signal read through a head, and the horizontal axis indicates an offset from the track center. Referring to FIG. 3, burst linearity is worst for the positive DC-erase method, better for the negative DC-erase method, and best for the AC-erase method. That is, asymmetry and distortion are reduced most by the AC-erase method.
In particular, the AC-erase method may be used in perpendicular magnetic recording (PMR) to prevent a read bias of a read head from being affected by magnetism remaining in a write head.
FIG. 4 is a schematic block diagram illustrating a conventional AC-erase method. Referring to FIG. 4, a write channel circuit 402 generates burst data 404 and high frequency AC data 406 and outputs the burst data 404 and high frequency AC data 406 to a pre-amplifier 408. The pre-amplifier 408 generates a write current and outputs the write current to a write head 410. The pre-amplifier 408 can generate the write current such that it corresponds to the burst data 404 and can alternatively generate the write current such that it corresponds to the high frequency AC data 406.
As illustrated in FIG. 4, in the conventional AC-erase method, the burst data 404 corresponding to bursts and the high frequency AC data 406 corresponding to a high frequency AC current are both generated by the write channel circuit 402.
In an HDD, the burst frequency is 1/(2T), wherein T is the period corresponding to the maximum write frequency. Thus, the burst frequency is correlated to the maximum frequency that data that can be recorded on a disk may have. In addition, operational characteristics of the write channel circuit 402 and the pre-amplifier 408 are correlated to (i.e., matched with) the period T, which is correlated to the maximum write frequency. Thus, when high frequency AC data 406 is generated by the write channel circuit 402, the maximum frequency the high frequency AC data 406 can have is 1/T (i.e., twice the burst frequency).
However, an increase in the storage density of a disk may require that the frequency of the high frequency AC data 406 be much higher than twice the burst frequency. Due to limitations of the write channel circuit 402 and the pre-amplifier 408, however, that requirement cannot be achieved using the conventional AC-erase method.
In addition, using the write channel circuit 402 to generate high frequency AC data having a frequency greater than twice the burst frequency would require a memory device for storing high frequency data and a high frequency clock signal generator, and thereby increase manufacturing cost.